[Bug c++/56037] New: Spurious syntax error triggered before ambiguity resolution of type-id

[Bug c++/56037] New: Spurious syntax error triggered before ambiguity resolution of type-id

[ricilake at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56037

             Bug #: 56037
           Summary: Spurious syntax error triggered before ambiguity
                    resolution of type-id
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ricilake@gmail.com


A spurious syntax error is produced by the following:

  static const int zero = 0;
  std::cout << (std::pair<int, int>(int(zero), int(zero))) << std::endl;

In contrast, 

  static const int zero = 0;
  static const int zero_alias = 0;
  std::cout << (std::pair<int, int>(int(zero), int(zero_alias))) << std::endl;

compiles correctly (assuming that there is an appropriate overload for
operator<<).

Section 8.2[2] states that 

The ambiguity arising from the similarity between a function-style cast and a  
type-id can occur in different contexts. The ambiguity appears as a choice
between a function-style cast expression and a declaration of a type. The
resolution is that any construct that could possibly be a type-id in its
syntactic context shall be considered a type-id.

In this case, 8.2[2] should not apply, since the syntactic context of the
parenthesized expression does not permit the production:

  cast-expression :: ( type-id ) cast-expression

However, in the first code excerpt, where the parenthesized expression would
not be a valid type-id (because of the redefinition of the parameter name), the
syntax error is apparently being triggered before the ambiguity resolution
decides that type-id is not possible. In the second code excerpt, the
parenthesize expression could contain a valid type-id, but ambiguity resolution
rejects that possibility.

---

Bug report generated as a result of
http://stackoverflow.com/questions/14403946/adding-parenthesis-to-a-constructor-call-causes-duplicate-parameter-error-in-xlc/14404900#14404900

[Bug c++/56037] Spurious syntax error triggered before ambiguity resolution of type-id

[ricilake at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56037

--- Comment #1 from ricilake at gmail dot com 2013-01-18 20:23:27 UTC ---
Created attachment 29214
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29214
Test cases as described in bug

[Bug c++/56037] Spurious syntax error triggered before ambiguity resolution of type-id

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56037

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-01-19
     Ever Confirmed|0                           |1

[Bug c++/56037] Spurious syntax error triggered before ambiguity resolution of type-id

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56037

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Reduced:

struct T
{
  T(int, int);
};

int main()
{
  static const int zero = 0;
  (T(int(zero), int(zero)));
}

[Bug c++/56037] Spurious syntax error triggered before ambiguity resolution of type-id

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56037

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This is closely related to PR29234. In fact, the patch I'm working on, as
linked from the latter, already fixes this bug too.

[Bug c++/56037] Spurious syntax error triggered before ambiguity resolution of type-id

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56037

--- Comment #4 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Sat Nov  2 09:34:13 2013
New Revision: 204312

URL: http://gcc.gnu.org/viewcvs?rev=204312&root=gcc&view=rev
Log:
/cp
2013-11-02  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/29234
    PR c++/56037
    * parser.c (cp_parser_cast_expression): If we aren't looking at
    a cast-expression don't call cp_parser_type_id.
    (cp_parser_postfix_expression): Likewise for compound-literal.
    (cp_parser_tokens_start_cast_expression): Adjust.

/testsuite
2013-11-02  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/29234
    PR c++/56037
    * g++.dg/parse/pr29234.C: New.
    * g++.dg/parse/pr56037.C: Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/parse/pr29234.C
    trunk/gcc/testsuite/g++.dg/parse/pr56037.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/parser.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/56037] Spurious syntax error triggered before ambiguity resolution of type-id

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56037

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.9.0

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed for 4.9.0.